Traditionalists will be popping the champagne corks - or at least sitting down for a nice cup of tea and a fondant fancy - at news from the University of Warwick. Researcher Nick Powdthavee has uncovered evidence that people are more satisfied with their lives if their partner is happy, but that this effect applies only to married couples, not those who opt for cohabitation over nuptial bliss.

"I had started working on the economics of happiness, which is a fairly new field," he says. "I've always had a curiosity about whether happiness is shared between people. We believe it to be true, instinctively, but there has been no chance to test it."

For his research, Powdthavee looked at results from the British household panel survey. "It's a survey that's been done for the last 12 years," he explains. "It questions the same people every year and it has all sorts of questions about work, marriage, health, and one on happiness, where you can rate your satisfaction with life. Because it's confidential, we can track how people, married or cohabiting, are affected by events in their partner's life."

To begin with, the results from both married and cohabiting couples were similar. "Change in levels of reported happiness had a similar correlation between partners in both types of relationship, but we couldn't tell from that if it was because one partner was made happy by the other's happiness, or if they were both sharing in the same material good fortune and were made equally, but independently, happy by that," Powdthavee says.

"What I wanted to examine was the effect on both people in a partnership when something happened to one of them that the other person was personally indifferent to. So, something like a pay rise isn't a good indicator. While it happens to one person, it can materially alter the lives of both, by bringing a higher standard of living.

"What I looked at was the level of satisfaction with their health that individuals reported on the survey. Health is a very personal thing and very rarely has a material impact on the partner of the person who is reporting dissatisfaction with their health - although obviously it might affect them emotionally."

This is where the controversial results appear. In married couples, the effect of a spouse's happiness is dramatic. A 30% increase in the spouse's life satisfaction score from the previous year can completely offset the negative impact of unemployment on the respondent's life satisfaction, for example. In cohabiting couples, however, the same results did not appear.

"I don't want to hypothesise about why that might be," says Powdthavee. "The results have already have got me into enough trouble! I don't have any strong explanations, but it is what the data showed. I'm absolutely not saying that on an individual level cohabiting relationships can't be as committed as marriages."

Powdthavee will shortly earn his PhD in economics, and will continue to work in the economics of happiness. "I'm currently working on the relationship between social capital, money and happiness," he says. "The early results show that money does increase happiness, but that the benefits of good relationships with friends, family and the community are worth much more to us in terms of affecting our personal happiness. And whereas we might imagine that rich people see more of their friends, it's not the case: they sacrifice those relationships for time in the office to earn more money.

"People make these decisions every day - time with their loved ones or time in the office - and often they choose the latter. But a more social life is much more valuable in happiness terms. I think most people know this, but they ignore it."